U.S. patent number 9,741,375 [Application Number 14/946,166] was granted by the patent office on 2017-08-22 for slider trailing edge contamination sensor.
This patent grant is currently assigned to SEAGATE TECHNOLOGY LLC. The grantee listed for this patent is Seagate Technology LLC. Invention is credited to Gary Joseph Kunkel, Narayanan Ramakrishnan.
United States Patent |
9,741,375 |
Kunkel , et al. |
August 22, 2017 |
Slider trailing edge contamination sensor
Abstract
A slider of a magnetic recording head has a leading edge, a
trailing edge, and an air bearing surface between the leading and
trailing edges. A sensor is situated at the trailing edge of the
slider and configured to sense presence of a lube droplet or other
contaminant at the trailing edge.
Inventors: |
Kunkel; Gary Joseph
(Minneapolis, MN), Ramakrishnan; Narayanan (Eden Prairie,
MN) |
Applicant: |
Name |
City |
State |
Country |
Type |
Seagate Technology LLC |
Cupertino |
CA |
US |
|
|
Assignee: |
SEAGATE TECHNOLOGY LLC
(Cupertino, CA)
|
Family
ID: |
58721014 |
Appl.
No.: |
14/946,166 |
Filed: |
November 19, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170148475 A1 |
May 25, 2017 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B
5/40 (20130101); G11B 5/607 (20130101); G11B
5/6017 (20130101); G11B 2005/0021 (20130101) |
Current International
Class: |
G11B
5/60 (20060101); G11B 5/40 (20060101) |
Field of
Search: |
;360/234-234.9 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Nov. 10, 2015, Lepkowski et al., "Designing RC Oscillator Circuits
with Low Voltage Operational Amplifiers and Comparators for
Precision Sensor Applications", On Semiconductor, printed from
internet on Nov. 10, 2015, 28 pages. cited by applicant.
|
Primary Examiner: Cao; Allen T
Attorney, Agent or Firm: Hollingsworth Davis, LLC
Claims
What is claimed is:
1. An apparatus, comprising: a slider of a magnetic recording head,
the slider having a leading edge, a trailing edge having an outside
edge, and an air bearing surface between the leading and trailing
edges; and a sensor situated at the outside edge of the trailing
edge of the slider, the sensor configured to sense presence of a
lube droplet or other contaminant at the outside edge of the
trailing edge.
2. The apparatus of claim 1, wherein the sensor comprises a
plurality of sensing elements.
3. The apparatus of claim 1, wherein the sensor comprises: a first
sensor situated at an active location of the outside edge of the
trailing edge where a lube droplet forms or other contaminant
accumulates; and a reference sensor situated away from the active
location.
4. The apparatus of claim 1, wherein adjacent sensing elements are
separated by a gap having a size related to a size of the lube
droplet.
5. The apparatus of claim 1, wherein the sensor comprises a thermal
sensor.
6. The apparatus of claim 1, wherein the sensor comprises an array
of thermal sensors arranged in one or more Wheatstone bridge
circuits.
7. The apparatus of claim 1, wherein the sensor comprises an open
circuit, wherein presence of the lube droplet closes the open
circuit.
8. The apparatus of claim 1, wherein the sensor comprises an RC or
RLC oscillator circuit configured to change an oscillation
frequency in response to sensing presence of the lube droplet or
other contaminant.
9. The apparatus of claim 1, wherein the sensor comprises a
capacitance sensor.
10. The apparatus of claim 1, wherein the sensor comprises an array
of capacitance sensors arranged in one or more Wheatstone bridge
circuits.
11. An apparatus, comprising: a slider of a magnetic recording
head, the slider having a leading edge, a trailing edge having an
outside edge, and an air bearing surface between the leading and
trailing edges; a sensor situated at the outside edge of the
trailing edge of the slider, the sensor configured to sense
presence of a lube droplet at the outside edge of the trailing
edge; and a detector coupled to the sensor, the detector configured
to generate a signal in response to the sensor sensing presence of
the lube droplet or other contaminant.
12. The apparatus of claim 11, wherein the detector comprises a
comparator configured to compare a signal produced by the sensor to
a reference signal indicative of a detection threshold.
13. The apparatus of claim 11, wherein: the sensor comprises a
capacitance sensor; and the detector is configured to convert a
capacitance of the capacitance sensor to a digital signal, and
compare the digital signal to a reference signal indicative of a
detection threshold.
14. The apparatus of claim 11, wherein the detector is configured
to detect closing of an open circuit of the sensor.
15. The apparatus of claim 11, wherein the sensor comprises one or
more of a thermal sensor, a capacitance sensor, and a sensor
configured to sense closing of an open circuit.
16. A method, comprising: providing relative movement between a
magnetic recording medium and a slider of a magnetic recording
head, the medium comprising a layer of lubrication and the slider
having a leading edge, a trailing edge having an outside edge, and
an air bearing surface between the leading and trailing edges; and
sensing presence of a lube droplet or other contaminant at the
outside edge of the trailing edge.
17. The method of claim 16, wherein sensing comprises sensing a
change in resistance at the outside edge of the trailing edge in
response to presence of the lube droplet or other contaminant.
18. The method of claim 16, wherein sensing comprises sensing a
change in capacitance at the outside edge of the trailing edge in
response to presence of the lube droplet or other contaminant.
19. The method of claim 16, wherein sensing comprises sensing
closing of an open circuit at the outside edge of the trailing edge
in response to presence of the lube droplet or other
contaminant.
20. The method of claim 16, wherein sensing comprises sensing a
change in frequency of an oscillator circuit in response to
presence of the lube droplet or other contaminant.
Description
SUMMARY
Embodiments of the disclosure are directed to an apparatus
comprising a slider of a magnetic recording head having a leading
edge, a trailing edge, and an air bearing surface between the
leading and trailing edges. A sensor is situated at the trailing
edge of the slider and configured to sense presence of a lube
droplet or other contaminant at the trailing edge.
Some embodiments are directed to an apparatus comprising a slider
of a magnetic recording head having a leading edge, a trailing
edge, and an air bearing surface between the leading and trailing
edges. A sensor is situated at the trailing edge of the slider and
configured to sense presence of a lube droplet at the trailing
edge. A detector is coupled to the sensor and configured to
generate a signal in response to the sensor sensing presence of the
lube droplet or other contaminant.
Other embodiments are directed to a method comprising providing
relative movement between a magnetic recording medium and a slider
of a magnetic recording head. The medium comprises a layer of
lubrication and the slider comprises a leading edge, a trailing
edge, and an air bearing surface between the leading and trailing
edges. The method also comprises sensing presence of a lube droplet
or other contaminant at the trailing edge.
The above summary is not intended to describe each embodiment or
every implementation. A more complete understanding will become
apparent and appreciated by referring to the following detailed
description and claims in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a slider in which the
various embodiments disclosed herein may be implemented;
FIG. 2 shows a recording head arrangement which incorporates a
sensor at the trailing edge of a slider in accordance with various
embodiments;
FIG. 3 is a flow chart of the method for detecting a lube droplet
or lube bridge in accordance with various embodiments;
FIG. 4 illustrates a slider which includes a sensor configured for
sensing a lube droplet or lube bridge at the trailing edge of the
slider in accordance with various embodiments;
FIG. 5 illustrates a slider which includes a sensor configured for
sensing a lube droplet or lube bridge at the trailing edge of the
slider in accordance with various embodiments;
FIG. 6 illustrates a slider which includes a sensor configured for
sensing a lube droplet or lube bridge at the trailing edge of the
slider in accordance with various embodiments;
FIG. 7 illustrates a slider which includes a thermal sensor
configured for sensing a lube droplet or lube bridge at the
trailing edge of the slider in accordance with various
embodiments;
FIG. 8 illustrates a slider which includes a thermal sensor
configured for sensing a lube droplet or lube bridge at the
trailing edge of the slider in accordance with various
embodiments;
FIG. 9 illustrates a slider which includes an electrical sensor
configured for sensing a lube droplet or lube bridge at the
trailing edge of the slider in accordance with various
embodiments;
FIG. 10 illustrates a slider which includes a capacitance sensor
configured for sensing a lube droplet or lube bridge at the
trailing edge of the slider in accordance with various
embodiments;
FIG. 11 illustrates a slider which includes a capacitance sensor
configured for sensing a lube droplet or lube bridge at the
trailing edge of the slider in accordance with various
embodiments;
FIG. 12 illustrates a slider which includes a capacitance sensor
configured for sensing a lube droplet or lube bridge at the
trailing edge of the slider in accordance with various
embodiments;
FIG. 13 illustrates an arrangement of thermal sensors that can be
implemented on a trailing edge of a slider in accordance with
various embodiments;
FIG. 14 illustrates an arrangement of capacitance sensors that can
be implemented on a trailing edge of a slider in accordance with
various embodiments;
FIG. 15 illustrates arrays of capacitance sensors that can be
implemented on a trailing edge of a slider in accordance with
various embodiments;
FIG. 16 illustrates a slider which includes a sensor configured for
sensing a lube droplet or lube bridge (or other contaminant) at a
trailing edge of a slider in accordance with some embodiments;
and
FIG. 17 illustrates a sensor configured for sensing a lube droplet
or lube bridge (or other contaminant) at a trailing edge of the
slider in accordance with some embodiments.
The figures are not necessarily to scale. Like numbers used in the
figures refer to like components. However, it will be understood
that the use of a number to refer to a component in a given figure
is not intended to limit the component in another figure labeled
with the same number.
DETAILED DESCRIPTION
The present disclosure generally relates to magnetic recording
devices used for data storage. Data storage systems may include one
or more transducers that respectively write, via a writer, and
read, via a reader, information to and from a magnetic storage
medium. The reader and writer are components disposed on an
aerodynamic slider of the magnetic recording transducer. It is
typically desirable to have a relatively small distance or
separation between a transducer and its associated media. This
distance or spacing is referred to herein as head-media separation.
By reducing the head-media separation, writers and readers are
generally better able to write and read data to and from a
recording medium, allowing for an increase in storage capacity
(e.g., tracks per inch or bits per inch). Reducing the head-media
separation, however, can result in accumulation of contaminants
(e.g., lubricant) on the surface of slider, in particular the
trailing edge of the slider, due to interaction between the slider
and a lubricant provided on a surface of the recording medium.
Turning now to FIG. 1, a side view of a slider 102 is illustrated.
The slider 102 includes a slider body 104 having a leading edge
113, a trailing edge 115, and an air bearing surface (ABS) 114
between the leading and trailing edges 113 and 115. The slider 102
also includes a transducer portion 106 provided within overcoat 108
at the trailing edge 115 of the slider 102. The slider 102 is
attached via suspension 110 to an arm 112. The ABS 114 of the
slider 102 is shown proximate the surface 116 of a magnetic
recording medium 118. During operation, a fly height 120 is
maintained between the slider 102 and the disk 118. A layer of
lubrication 117 is shown covering the surface 116 of the medium
118. The lubricant 117 (referred to herein as lube) is typically
applied to the medium surface 116 as a molecularly thin-film (e.g.,
a thickness from 10 to 50 Angstroms), and serves to reduce wear of
the surface 116 due to contact with the slider 102.
Perfluoropolyethers (PFPEs) are often used as an effective
lubricant for thin-film recording media.
FIG. 2 shows a recording head arrangement 200 in accordance with
various embodiments. The recording head arrangement 200 includes a
slider 102 positioned proximate a rotating magnetic recording
medium 118. The slider 102 includes a reader 220 and a writer 230
proximate the ABS 114 for respectively reading and writing data
from/to the magnetic recording medium 118. The writer 230 includes
a corresponding heater 235, and the reader 220 also includes a
corresponding heater 225 according to various embodiments. The
writer heater 235 can be powered to cause protrusion of the ABS 114
predominately in the ABS region at or proximate the writer 230 and
the reader heater 225 can be powered to cause protrusion of the ABS
114 predominately in the ABS region at or proximate the reader 220.
Activation of both the writer and reader heaters 235 and 225 causes
protrusion of the pole tip region of the slider 102. Power can be
controllably delivered independently to the heaters 225 and 235 to
adjust the fly height (e.g., clearance) of the slider 102 relative
to the surface of the recording medium 118.
According to some embodiments, the recording head arrangement 200
can be configured for heat-assisted magnetic recording (HAMR). HAMR
generally refers to the concept of locally heating a magnetic
recording medium to reduce coercivity at the heated location. This
allows the applied magnetic writing fields to more easily direct
the magnetization during the temporary magnetic softening of the
medium caused by the heat source. HAMR allows for the use of small
grain media, with a larger magnetic anisotropy at room temperature
to assure sufficient thermal stability, which is desirable for
recording at increased areal densities. HAMR can be applied to any
type of magnetic storage media including tilted media, longitudinal
media, perpendicular media, and patterned media. By heating the
media, the coercivity is reduced such that the magnetic write field
is sufficient to write to the media. Once the media cools to
ambient temperature, the coercivity has a sufficiently high value
to assure thermal stability of the recorded information.
In order to achieve desired data density, a HAMR recording head
includes optical components that direct light from a light source
210, such as a laser diode, to the recording medium 118 via an
optical waveguide 214. The light source 210 can be mounted
external, or integral, to the slider 102. It is desirable that the
HAMR media hotspot be smaller than a half-wavelength of light
available from current sources (e.g., laser diodes). Due to what is
known as the diffraction limit, optical components cannot focus the
light at this scale. One way to achieve tiny confined hot spots is
to use an NFT 240, such as a plasmonic optical antenna. The NFT 240
is designed to support local surface-plasmon at a designed light
wavelength. At resonance, high electric field surrounds the NFT 240
due to the collective oscillation of electrons in the metal. Part
of the field will tunnel into the medium 118 and get absorbed,
raising the temperature of the medium locally for recording. During
recording, a write pole of the writer 230 applies a magnetic field
to the heated portion of the medium 118. The heat lowers the
magnetic coercivity of the media, allowing the applied field to
change the magnetic orientation of heated portion. The magnetic
orientation of the heated portion determines whether a one or a
zero is recorded. By varying the magnetic field applied to the
magnetic recording medium 118 while it is moving, data is encoded
onto the medium 118. It is understood that embodiments of the
disclosure may be implemented in a wide variety of recording heads,
including those configured for conventional magnetic recording or
HAMR.
The slider 102 includes a number of bond pads (not shown in FIG. 2,
but see FIGS. 4-11) on the trailing edge of the slider 102. These
bond pads are connected through the overcoat 108 to various
components, e.g., reader, writer, heaters, sensors, etc. of the
slider 102. The current industry standard of nine pads include bond
pads R+ and R- for the reader, W+ and W- for the writer, GND for
ground (which defines the ground potential of the slider body 102),
Sensor+ and Sensor- for the temperature sensor (e.g., a dual-ended
coefficient of resistance temperature sensor or DETCR), and HTR1
and HTR2 for the writer and reader heaters, respectively. During
fabrication of a slider 102, the bond pads 250 are electrically
connected to the electrical connections (e.g., traces) along the
suspension 110 (shown in FIG. 1). It should be noted that more or
less bond pads may be used as appropriate to a specific
application, e.g., the need for a dedicated bond pad, additional
bond pads to accommodate additional readers, writers, heaters,
sensors or other components, additional bond pads to accommodate a
heat-assisted magnetic recording (HAMR) laser, etc.
The representative slider 102 of FIG. 2 is shown to include an
accumulation of lubricant or lube 270 at the trailing edge 115. As
the slider 102 files over the surface of the recording medium 118,
the slider 102 interacts with the lube 117 and hydrocarbon
contaminants on the medium 118. Over time, the lube 117 and
contaminants transfers to the slider 102 and accumulate on the
trailing edge 115 of the slider 102. Droplets 272 of the lube 117
(alone or with other contaminants) can form on the trailing edge
115. The size of lube droplets 272 varies widely, but are generally
observed within a range of between about 0.1 .mu.m to about 100
.mu.m. Larger droplet (>100 microns) are also observed in some
instances, depending on drive operating cycle and history as well
as air bearing design. Typical lube droplets 272 that form on the
trailing edge 115 have a size (e.g., diameter or cross-sectional
dimension) ranging between about 20 and 30 .mu.m. If the droplets
272 grow large enough, the droplets 272 can form a lube bridge on
the trailing edge 115 or drop off of the slider 102 and settle on
the surface of the recording medium 118 (more specifically, on the
lube surface 117). For simplicity of explanation, the term "lube
droplet" can also encompass the term "lube bridge." Although these
formations differ, the term "lube droplet" is used interchangeably
with "lube bridge" throughout this disclosure.
In some instances, the lube droplets 272 that settle on the medium
118 can spread back onto the lubrication layer 117 of the medium
118 or are sheared off by air shear or by contact with the slider
102. In other instances, however, the recording head arrangement
200 may be performing a write operation at the same time the slider
102 encounters a lube droplet 272 protruding from the surface of
the recording medium 118. In such instances, a significant vertical
excursion of the slider 102 takes place, and the signal is not
properly written to the surface of the recording medium 118. More
specifically, the data is written with the slider 102 at an
abnormally large head-medium spacing which causes incomplete
overwrite of old data and results in a skip-write error. Contact
between the slider 102 and a protruding lube droplet 272 can also
result in undesirable excitation of slider 102 at a resonance
frequency. This undesirable slider excitation can cause flying
height modulation resulting in poor writing.
FIG. 2 further shows a sensor 260 situated at the trailing edge 115
of the slider. The sensor 260 is configured to sense presence of a
lube droplet 272 or a lube bridge (or other contamination) at the
trailing edge 115. A detector 215, coupled to the sensor 260, can
be configured to detect presence of the lube droplet 272 or lube
bridge in response to a signal produced by the sensor 260. For
example, the detector 215 can be configured to compare the signal
produced by the sensor 260 to a reference signal (e.g., a detection
threshold signal). The reference signal used by the detector 215
can be indicative of detection threshold developed as a predefined
percentage change (e.g., >2%, 5%, or 10% change) in the sensor
signal, for example. If the sensor signal exceeds the reference
signal (e.g., in magnitude) by a predetermined threshold, detection
of a lube droplet 272 or lube bridge is declared. Various forms of
corrective action can then be carried out to address the presence
of a lube droplet 272 or lube bridge detected on the trailing edge
115 of the slider 102.
According to some embodiments, the sensor 260 comprises a single
sensing element. In other embodiments, the sensor 260 comprises a
multiplicity of sensing elements, such as an array of elements. For
example, the sensor 260 can be implemented to include one or an
array of thermal sensors. In other embodiments, the sensor to 260
can be implemented to include one or an array of capacitance
sensors. In further embodiments, the sensor 260 can be implemented
to include one or more open circuits, wherein presence of a lube
droplet or lube bridge closes one or more of the open circuits.
FIG. 3 is a flow chart of the detection method that can be
implemented using the sensor 260 shown in FIG. 2. The method of
FIG. 3 involves providing 302 relative movement between a magnetic
recording medium and the slider. The method also involves sensing
304 presence of a lube droplet at the trailing edge of the slider.
In some embodiments, the method further involves producing 306 a
signal in response to sensing presence of the lube droplet. In
further embodiments, the method can also involve taking remedial
action 308 in response to the signal. For example, various
operations can be performed to break up or change the lube droplet
or lube bridge on the trailing edge of the slider. Representative
remedial operations include performing a fast sweep, stop dwelling
on the current track, or performing a load/unload of the head
(e.g., read/write operations are suspended, the head is unloaded
and parked over the ramp until the issue is resolved)
operation.
FIG. 4 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or lube bridge at the
trailing edge 115 of the slider 102 in accordance with various
embodiments. In the embodiment shown in FIG. 4, the sensor 260 is
formed as a metal wire or trace at the trailing edge 115 of the
slider 102. The sensor 260 can be implemented as a thermal sensor
and configured to monitor changes in heat transfer to/from the
sensor 260. Suitable materials for fabricating the sensor 260
include NiFe, Ni, Ru, Cr, W and other materials that have a
relatively high thermal coefficient of resistance (TCR). According
to various embodiments, the sensor 260 can have a length, l, of
between about 0.1 and 100 .mu.m, such as between about 20 and 30
.mu.m. The sensor 260 can have a width, w, or diameter of between
about 0.1 and 100 .mu.m, such as between 0.5 and 5 .mu.m. The
sensor 260 can have the depth of about 100 nm, such as between 40
and 80 nm. The trade-off between increased sensitivity to detecting
smaller size droplets versus the need for increased number of
elements in the sensor array using shorter length or smaller width
sensors would be considered in practice. In some embodiments, the
sensor 260 is formed as a thin-film sensor, rather than a wire or a
trace. In such embodiments, the thin-film sensor 260 can have a
thickness of between about 10 nm and 100 nm, for example. In some
embodiments, a single sensing element can run along the entire
width of the slider (along the trailing edge), i.e., length
(l).about.slider width.
FIG. 5 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or lube bridge at the
trailing edge 115 of the slider 102 in accordance with various
embodiments. In the embodiment shown in FIG. 5, the sensor 260
comprises a multiplicity of sensing elements, E1-En. In some
embodiments, individual sensing elements E1-En are configured to
sense the presence of a lube droplet 272 or lube bridge in response
to contact with the lube droplet 272 or lube bridge. For example,
sensing element E3 shown in FIG. 5 senses presence of a lube
droplet 272a in response to the lube droplet 272a contacting the
sensing element E3. It is noted that a lube droplet 272 or lube
bridge generally grows in size over time and may be sensed by the
sensing element E3 after achieving a relatively large size (e.g.,
.about.10-15 .mu.m or larger).
In other embodiments, pairs of sensing elements E1-En are
configured to sense the presence of a lube droplet 272 or lube
bridge in response to contact between the lube droplet/bridge 272
and a pair of sensing elements. In such embodiments, a gap, g, is
provided between adjacent sensing elements E1-En and sized to allow
for detection of a lube droplet 272 having a predetermined range of
size. For example, the lube droplet 272b shown in FIG. 5 is at
least partially captured within a gap, g, provided between sensing
elements E1 and E2. By way of illustration and not of limitation, a
lube droplet of interest may have a predetermined size of between
20 and 30 .mu.m. The gap, g, can be dimensioned to be somewhat
smaller than the predetermined size of the lube droplet of
interest, such as about 15 .mu.m. The gap, g, is preferably sized
to allow at least partial capture of a lube droplet of interest
while allowing the lube droplet contact adjacent sensing elements.
For example, lube droplet 272b shown in FIG. 5 is partially
captured within the gap, g, while contacting both sensing elements
E1 and E2. The sensor 260 senses the presence of the lube droplet
272b in contact with both sensing elements E1 and E2, such as by
sensing a change in resistance. For example, contact with sensing
elements E1 and E2 by the lube droplet 272b can cause shorting
between the pair of sensing elements, resulting in a reduction in
resistance of the sensor 260.
According to other embodiments, the gap can be sized to allow full
capture of a lube droplet of interest between adjacent sensing
elements. The gap, g.sub.2, shown between sensing elements E3 and
En, for example, has a size greater than the width or diameter of
the lube droplet 272c of interest. For example, the lube droplet
272c of interest may have a size ranging between about 20 and 40
.mu.m, and the gap, g.sub.2, may have a size of at least 45 to 50
.mu.m. The sensor 260 can sense the presence of the lube droplet
272c falling between adjacent sensing elements E3 and En by sensing
a change in capacitance between sensing elements E3 and En. It is
noted that one or a combination of these sensing approaches can be
implemented by the sensor 260. For example, the sensor 260 can be
implemented to sense a change of resistance of individual sensing
elements, a change of resistance between adjacent sensing elements,
a change of capacitance between adjacent sensing elements, or any
combination of these sensing approaches.
FIG. 6 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or a lube bridge at the
trailing edge 115 of the slider 102 in accordance with various
embodiments. The sensor 260 shown in FIG. 6 includes a
two-dimensional array of sensing elements, E1-En, situated on the
trailing edge 115 of the slider 102. Implementing the sensor 260 is
a two-dimensional array of sensing elements increases the effective
surface area that is capable of sensing formation of lube droplets
and lube bridges on the trailing edge 115 of the slider 102. The
sensor 260 shown in FIG. 6 can be implemented in the various
manners described previously with regard to FIG. 5.
FIG. 7 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or lube bridge at a trailing
edge 115 of the slider 102 in accordance with some embodiments. The
sensor 260 shown in FIG. 7 is implemented as a thermal sensor
comprising a single sensing element. For example, the sensor 260
can be implemented as a wire or trace having a relatively high TCR
(or a thin film element). One end of the sensor 260 is coupled to a
first bond pad 250 (P6), and the other end of the sensor 260 is
coupled to a second bond pad 250 (P9). A detector 215 is coupled to
the slider 102 and, more particularly, coupled to the sensor 260.
The sensor 260 is biased by the bond pads P6 and P9, preferably
with a constant current (DC), such that the sensor 260 is hotter
than ambient temperature. The sensor 260 is configured to measure a
change in heat transfer due to the presence of a lube droplet 272
or lube bridge.
Formation of a lube droplet 272 or lube bridge at the sensor 260
changes the heat transfer boundary condition of the sensor 260,
resulting in cooling of the sensor 260. This cooling of the sensor
260 causes a change in resistance in the sensor 260 and a
corresponding voltage change across the bond pads P6 and P9. This
voltage change can be detected by the detector 215. The detector
215 can include a comparator 217 which receives an output signal
from the sensor 260 (e.g., a voltage change across bond pads P6 and
P9) and compares the sensor signal with a reference signal or
value. The reference signal or value can be a signal/value
indicative of a predetermined detection threshold. For example, the
detector 215 can be configured to detect a percentage change in the
output signal of the sensor 216, such as a 2%, 5%, or 10%
change.
FIG. 8 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or a lube bridge at a
trailing edge 115 of the slider 102 in accordance with various
embodiments. The sensor 260 shown in FIG. 8 is implemented as a
thermal sensor comprising an array of sensing elements, E1-En. Each
of the sensing elements, E1-En, can be implemented as a wire or
trace having a relatively high TCR. In other embodiments, the
sensing elements, E1-En, can be implemented as thin-film elements.
The length, width, and depth of the sensing elements E1-En and the
gap between sensing elements can be determined based on the size of
the lube droplets and/or lube bridges of interest. One end of the
sensor array 260 is coupled to a first bond pad 250 (P1) and the
other end of the sensor array 260 is coupled to a second bond pad
250 (P9). In some embodiments, the sensing elements, E1-En, are
connected in series. In other embodiments, the sensing elements,
E1-En, are connected in parallel.
In a manner similar to that described in FIG. 7, formation of a
lube droplet 272 or lube bridge at one or more of the sensing
elements E1-En changes the heat transfer boundary condition of the
sensing element(s), resulting in cooling of the sensing element(s).
Cooling of the one or more sensing elements causes a change in
resistance in the sensor 260 and a corresponding voltage change
across the bond pads P1 and P9. This voltage change can be detected
by the detector 215.
FIG. 9 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or a lube bridge at a
trailing edge 115 of the slider 102 in accordance with various
embodiments. The sensor 260 shown in FIG. 9 differs from the
sensors described previously with regard to FIGS. 7 and 8 in terms
of structure and function. The sensor 260 shown in FIG. 9 is
configured to sense electrical continuity between adjacent sensing
elements E1-En due to the presence of a lube droplet or a lube
bridge, rather than changes in heat transfer from the sensor
elements. The sensor 260 of FIG. 9 includes a multiplicity of
electrically conductive sensing elements, E1-En, with a gap, g,
provided between adjacent sensing elements. The gap, g, is sized
such that a lube droplet 272 can fall at least partially between a
pair of the sensing elements, E1-EN, but remain in contact with the
pair of sensing elements. For example, the lube droplet 272 shown
in FIG. 9 is captured at least partially between sensing elements
E4 and En, but remains in physical contact with each of elements E4
and En.
The sensing elements, E1-En, of the sensor 260 are connected such
that alternating sensing elements are connected to different
electrical circuits. For example, sensing elements E1, E3, and En
are connected in series to a first circuit that is coupled to bond
pads P1 and P9, which bias these sensing elements of the sensor
260. Intervening sensing elements E2 and E4, however, are connected
to a second circuit that is coupled to a ground pad, P5. Formation
of a lube droplet or a lube bridge between adjacent sensing
elements, such as droplet 272 formed between sensing elements E4
and En, closes the circuit between sensing elements E4 and En,
causing electrical shorting between these sensing elements.
Development of a short-circuit (or a reduction in resistance)
within the sensor 260 can be readily detected by the detector 215
as a reduction in voltage across bond pads P1 and P9.
In another embodiment (cf. FIG. 5), a sinusoidal voltage or current
input can be applied at a different frequency across of each of the
sensor elements (E1, E2, . . . En) and the sensed output signal can
be combined, multiplexed and process to detect accumulation of
droplets as well as the location(s) of droplet accumulation.
FIG. 10 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or a lube bridge at a
trailing edge 115 of the slider 102 in accordance with various
embodiments. The sensor 260 shown in FIG. 10 is configured as a
capacitance sensor. The sensor 216 includes a first conductor 262
spaced apart from a second conductor 264. The first conductor 262
is coupled to a first bond pad 250 (P6). The second conductor 264
is coupled to a second bond pad 250 (P9). Air serves as a
dielectric between the two conductors 262 and 264. The capacitance
between the first and second conductors 262 and 264 can be measured
and stored in the detector 215 as a reference capacitance.
According to some embodiments, and using the length, width, and
depth references shown in FIG. 4, the conductors 262 and 264 can
have a length of between about 100 nm and 10 .mu.m, a width of
between about 5 .mu.m and 20 .mu.m, and a depth of between about 10
.mu.m and 40 .mu.m. According to various embodiments, each of the
conductors 262 and 264 can have a surface area of between about 50
.mu.m.sup.2 and 800 .mu.m.sup.2. If necessary, the depth can be
increased further (not geometrically constrained) to increase
surface area of the conductors/electrodes. Further, the width can
also be increased beyond the stated 20 .mu.m with alternate bond
pad layouts.
Formation of a lube droplet 272 or a lube bridge between the first
and second conductors 262 and 264 changes the composition of the
dielectric between the conductors 262 and 264. For example, the
dielectric constant can change from .about.1.0 for air to
.about.2-3, which is typical for perfluoropolyether (PFPE)
lubricants. This change in the dielectric composition due to the
presence of the lube droplet 272 or lube bridge causes a change in
the capacitance of the sensor 260. This change in capacitance
sensed by the sensor 260 can be detected by the detector 215. For
example, the detector 215 can be configured to compare the changed
capacitance of the sensor 260 with a previously stored reference
capacitance 219 (with no lube present between the conductors 262
and 264). A deviation beyond a predetermined threshold (e.g., a
percentage difference of 2%, 5%, or 10%) between the two
capacitance values indicates presence of a lube droplet 272 or do
bridge at the trailing edge 115 of the slider 102.
According to some embodiments, the detector 215 is implemented as
part of a preamp of a hard disk drive which incorporates the
capacitance sensor 260 shown in FIG. 10. The preamp can include an
integrated capacitive-to-digital converter which receives an analog
signal produced by capacitance sensor 260 and converts this signal
to a digital signal. The digital signal can be compared to the
previously stored reference capacitance, which can be stored in a
memory of the preamp. It is noted that capacitive sensing of lube
droplets or lube bridges using the sensor 260 shown in FIG. 10 is
highly immune to spacing dependence of the slider 102 relative to a
magnetic recording medium.
FIG. 11 illustrates a slider 102 which includes a multiplicity of
the capacitance sensors 260 shown in FIG. 10. Although the
capacitance sensor 260 shown in FIG. 11 includes a multiplicity of
individual capacitive sensing elements (e.g., C1 and C2), the
capacitance sensor 260 only requires two bond pads (e.g., bond pads
P7 and P8) for proper operation. Each capacitive sensing element,
C1 and C2, includes a first conductor coupled to one of the bond
pads (P7) and a second conductor coupled to another bond pad (P8).
Although two capacitive sensing elements (C1 and C2) are shown in
FIG. 11, it is understood that any number of capacitive sensing
elements can be implemented in the capacitance sensor 260 shown in
FIG. 11. Sensing of one or more lube droplets or lube bridges can
be sensed by the sensor 260 in a manner described previously with
regard to FIG. 10.
FIG. 12 illustrates an arrangement of capacitance sensors that can
be implemented on a trailing edge of a slider in accordance with
various embodiments. The capacitance sensors, C.sub.0, C.sub.1,
C.sub.2, can be arranged to form a Wheatstone bridge with an output
coupled to an operational amplifier 1200. Nominally, C.sub.0 would
be set equal to C.sub.1 and C.sub.2 when no contaminant/lube
droplets are present at the trailing edge face (baseline). In this
state, the bridge circuit of FIG. 12 would be balanced ideally with
zero sense signal output. In FIG. 12, two capacitive sensing
elements, C1 and C2, are illustrated as having a variable
capacitance. Each of sensing elements C1 and C2 is configured to
sense for formation of a lube droplet or a lube bridge at the
trailing edge of a slider. Capacitive sensing elements C.sub.0 have
a fixed known capacitance. A reference voltage, V.sub.ref, is
provided to the bridge by a first bond pad and the opposite leg of
the bridge is coupled to a ground pad. The operational amplifier
1200 can be part of a detector (situated away from the trailing
edge of the slider), which produces an output signal, V.sub.sig, in
response to changes in capacitance of either of the two capacitive
sensing elements C.sub.1 and C.sub.2. The output signal, V.sub.sig,
can be compared to a reference signal to detect formation of a lube
droplet or lube bridge at the trailing edge of the slider. The
bridge circuit configuration shown in FIG. 12 increases the
sensitivity of droplet detection manifold, since in such a scheme
only the change in capacitance would be amplified and sensed. In
some embodiments, a multiplicity of the Wheatstone bridge circuits
shown in FIG. 12 can be connected in series to form larger
capacitance sensor arrays.
FIG. 13 illustrates an arrangement of thermal sensors (e.g.,
resistive temperature sensors) that can be implemented on a
trailing edge of a slider in accordance with various embodiments.
Similar to the configuration shown in FIG. 12, the thermal sensors,
R.sub.0, R.sub.1, R.sub.2, can be arranged to form a Wheatstone
bridge with an output coupled to an operational amplifier 1300
(situated away from the trailing edge of the slider). Nominally,
R.sub.0 would be set equal to R.sub.1 and R.sub.2 when no
contaminant/lube droplets are present at the trailing edge face
(baseline). In this state, the bridge circuit of FIG. 13 would be
balanced ideally with zero sense signal output. In FIG. 13, two
resistive sensing elements, R1 and R2, are illustrated as having a
variable resistance. Each of resistive sensing elements R1 and R2
is configured to sense for formation of a lube droplet or a lube
bridge at the trailing edge of a slider. Resistive sensing elements
R.sub.0 have a fixed known resistance. A reference voltage,
V.sub.ref, is provided to the bridge by a first bond pad and the
opposite leg of the bridge is coupled to a ground pad. The
operational amplifier 1300 can be part of a detector, which
produces an output signal, V.sub.sig, in response to changes in
resistance of either of the two resistive sensing elements R.sub.1
and R.sub.2. The output signal, V.sub.sig, can be compared to a
reference signal to detect formation of a lube droplet or lube
bridge at the trailing edge of the slider. The bridge circuit
configuration shown in FIG. 13 increases the sensitivity of droplet
detection manifold, since in such a scheme only the change in
resistance would be amplified and sensed. In some embodiments, a
multiplicity of the Wheatstone bridge circuits shown in FIG. 13 can
be connected in series to form larger resistive sensor arrays.
FIG. 14 illustrates an arrangement of capacitance sensors that can
be implemented on a trailing edge of a slider in accordance with
various embodiments. The capacitance sensors C.sub.1, C.sub.2,
C.sub.3, and C.sub.4 are arranged to form a Wheatstone bridge with
an output coupled to an operational amplifier 1400 (situated away
from the trailing edge of the slider). In the embodiment of FIG.
14, each of the capacitance sensors C.sub.1, C.sub.2, C.sub.3, and
C.sub.4 is configured to sense formation of a lube droplet or lube
bridge (or other contaminant). A change in capacitance across any
one of the capacitance sensors C.sub.1, C.sub.2, C.sub.3, and
C.sub.4 due to presence of a lube droplet/bridge or other
contaminant results in development of a sensed voltage,
V.sub.sense, at the output of the sensing arrangement. The sensor
embodiment illustrated in FIG. 14 is conservative on bond pads and
provides differential sensing so that common-mode noise rejection
is inherently performed.
According to an alternative embodiment, the sensor arrangement
shown in FIG. 14 can be populated with resistive temperature
sensors (e.g., DETCRs) instead of capacitance sensors. In such an
embodiment, capacitance sensors C.sub.1, C.sub.2, C.sub.3, and
C.sub.4 would be replaced by resistive temperature sensors R.sub.1,
R.sub.2, R.sub.3, and R.sub.4. A change in resistance across any
one of the resistive temperature sensors R.sub.1, R.sub.2, R.sub.3,
and R.sub.4 due to presence of a lube droplet/bridge or other
contaminant results in development of a sensed voltage,
V.sub.sense, at the output of the sensing arrangement.
FIG. 15 illustrates an arrangement of capacitance sensors that can
be implemented on a trailing edge of a slider in accordance with
various embodiments. FIG. 15 shows a large array of capacitance
sensor C1-C8 arranged in two Wheatstone bridges 1 and 2 each driven
by an input, V.sub.inp. Each bridge 1 and 2 has an output coupled
to a respective operational amplifier 1502 and 1504 (situated away
from the trailing edge of the slider). In some embodiments, the
outputs, V.sub.sense 1 and V.sub.sense 2, of the operational
amplifiers 1502 and 1504 can be analyzed separated for a change in
sensed voltage. In other embodiments, the outputs, V.sub.sense 1
and V.sub.sense 2, of the operational amplifiers 1502 and 1504 can
be applied to a summer 1506 whose output, V.sub.sense, can be
analyzed for a change in sensed voltage. The sensor embodiment
illustrated in FIG. 15 is conservative on bond pads and provides
differential sensing so that common-mode noise rejection is
inherently performed. In an alternative embodiment, the capacitance
sensors C.sub.1-C.sub.8 can be replaced by resistive temperature
sensors R.sub.1-R.sub.8.
FIG. 16 illustrates a slider 102 which includes a sensor 260
configured for sensing a lube droplet or lube bridge (or other
contaminant) at a trailing edge 115 of the slider 102 in accordance
with some embodiments. The sensor 260 shown in FIG. 16 is
implemented to include a first sensor, S.sub.1, and a reference
sensor, S.sub.ref. The first sensor, S.sub.1, is situated at a
location of the trailing edge 115 where lube droplets/bridges
actively form (or other contaminants accumulate). The reference
sensor, S.sub.ref, is situated at a location of the trailing edge
115 where lube droplets/bridges/contaminants do not actively
form/accumulate, such as above the bond pads 250. In some
embodiments, the first sensor, S.sub.1, and the reference sensor,
S.sub.ref, are resistive temperature sensors. In other embodiments,
the first sensor, S.sub.1, and the reference sensor, S.sub.ref, are
capacitance sensors.
In the representative embodiment shown in FIG. 16, the first
sensor, S.sub.1, is coupled to bond pads P2 and P3, and the
reference sensor, S.sub.ref, is coupled to bond pads P3 and P5. In
this representative example, the two sensors, S.sub.1 and
S.sub.ref, share a common bond pad (i.e., bond pad P3). The sensor
260 is coupled to a detector 215 which typically resides away from
the slider 102 (e.g., within the hard drive electronics). The
detector 215 includes a first operational amplifier 1602 with
inputs coupled to bond pads P2 and P3 respectively. A second
operational amplifier 1604 of the detector 215 has inputs coupled
to bond pads P3 and P5. Outputs of the first and second operational
amplifiers 1602 and 1604 are respectively coupled to a summer 1606
having an output where a sensed voltage, V.sub.sense, is
provided.
The sensing arrangement shown in FIG. 16 provides differential
sensing by the first sensor, S.sub.1, relative to the reference
sensor, S.sub.ref. This arrangement provides common-mode noise
rejection and compensation for the effect of changes in ambient
drive temperature, humidity, pressure (altitude), etc. It is
understood that a multiplicity of sensors, S.sub.1-S.sub.n, can be
implemented in the embodiment shown in FIG. 16, and that a single
sensor, S1, is shown for purposes of simplicity of explanation
(see, e.g., sensor 260 shown in FIG. 9).
FIG. 17 illustrates a sensor 260 configured for sensing a lube
droplet or lube bridge (or other contaminant) at a trailing edge of
the slider in accordance with some embodiments. The sensor 260
includes capacitance sensors that can be part of an RC or RLC
oscillator circuit. According to such embodiments, a change in
capacitance due to lube droplet/contaminant accumulation between
the conductors of the capacitance sensor can be sensed through a
change in resonant frequency of the oscillator circuit using a
tunable resistor. Alternatively, the resonance change can be
detected using a frequency sweep with a fixed R (and L) value.
In the embodiment shown in FIG. 17, an RC oscillator circuit
includes a sensor 260 coupled to an RC operational amplifier
oscillator 1702. The sensor 206 includes a first capacitance
sensor, C.sub.Sen, and a reference capacitance sensor, C.sub.Ref.
The first capacitance sensor, C.sub.Sen, is situated at a location
of the slider's trailing edge where lube
droplets/bridges/contaminants are expected to form/accumulate. The
reference capacitance sensor, C.sub.Ref, is situated at a location
of the slider's trailing edge where lube
droplets/bridges/contaminants are not expected to form/accumulate,
such as above the bond pads. The first capacitance sensor,
C.sub.Sen, and the reference capacitance sensor, C.sub.REF, are
coupled to the RC oscillator 1702, which resides off of the slider
(e.g., in the hard drive electronics). The oscillation frequency
changes in response to accumulation of lube between the conductors
of the first capacitance sensor, C.sub.Sen.
The oscillation frequency can be determined by counting, by a
counter circuit 1706, the number of clock pulses (i.e. MHz) in a
time window that is formed by the square wave oscillator output
(i.e. kHz) of a comparator circuit 1704. The counter circuit 1706
can be implemented with a digital logic counter circuit or by using
the Time Processing Unit (TPU) channel of a microprocessor 1720. It
is noted that, other than the sensor 260, all other components
shown in FIG. 17 are located off of the slider, such as in the hard
drive electronics. If desired, temperature correction can be
accomplished by implementing a curve fitting routine with data
obtained by calibrating the sensor 260 over the expected operating
range. It will be appreciated that other RC and RLC oscillator
circuits are contemplated, and the representative example shown in
FIG. 17 is provided for non-limiting illustrative purposes.
Systems, devices or methods disclosed herein may include one or
more of the features structures, methods, or combination thereof
described herein. For example, a device or method may be
implemented to include one or more of the features and/or processes
above. It is intended that such device or method need not include
all of the features and/or processes described herein, but may be
implemented to include selected features and/or processes that
provide useful structures and/or functionality.
Various modifications and additions can be made to the disclosed
embodiments discussed above. Accordingly, the scope of the present
disclosure should not be limited by the particular embodiments
described above, but should be defined only by the claims set forth
below and equivalents thereof.
* * * * *